Methods industrially carried out for epoxidation generally employ chlorohydrin, organic peroxide, hydrogen peroxide or like oxidizing agents. However, these methods inevitably pose problems of requiring multi-stage reaction and generating by-products.
It is more convenient to convert unsaturated hydrocarbon to the corresponding epoxide using molecular oxygen as an oxidizing agent. However, this technique has been employed on an industrial scale only for the production of ethylene oxide from ethylene. The production of an epoxide from other unsaturated hydrocarbon, for example, propylene oxide directly from propylene by oxidation with oxygen, is very difficult to accomplish. Some methods for oxidation of propylene directly to propylene oxide with oxygen were proposed in publications (Japanese Examined Patent Publication No.39404/1978, Japanese Unexamined Patent Publication No.97378/1995, etc.). However, all of the proposed methods raise problems of low selectivity, low activity and other defects from the viewpoint of efficiency.
Proposed methods of producing an epoxide from unsaturated hydrocarbon with a high selectivity include methods comprising partially oxidizing unsaturated hydrocarbon in the presence of molecular hydrogen using a catalyst comprising gold and titanium oxide (Japanese Unexamined Patent Publications No. 127550/1996 and No.5590/1998). Yet, the proposed methods are problematic in that although active in some degree in the initial stage of reaction, the catalyst lowers its activity with time and shows an insufficient activity in a stationary state.